Posts Tagged ‘radiators’

A Passivhaus (Passive House) renovation?

passivhaus_thermogram_gedaemmt_ungedaemmt

The picture on the left is a thermograph – showing the difference in lost heat between a conventional house (on the left) and a house built to PassivHaus standards (on the right). Which house would you rather be living in when Russia cuts gas supplies

The PassivHaus standard, as interpreted for the UK by the AECB, should result in an 80% reduction in a house’s energy consumption. PassivHaus design concentrates on three areas: improving the air-tightness of the house, reducing heat bridges, and, to a lesser extent, considering heat gain from the sun.

In essence, a typical passivhaus is air-tight & super-insulated, with mechanical ventilation with heat recovery (referred to as MVHR) to solve the issue of internal air quality. I had always believed that a PassivHaus needed no extra heating, but apparently that’s not entirely true. While they’ll generally have no radiators or underfloor heating, they often do have a small heating element within the ventilation system. In general they require about 30cm of insulation, and windows that are triple glazed.

Here are some of the key points of interest to me from the AECB version of the standard:

  • Use daylight to displace use of electric light
  • Solar hot water system required to deliver at least 50% of hot water
  • Walls, Floors, and Roof to all have U values of <= 0.15W/m2K
  • Doors (uninstalled) should have a U value of <= 0.6 W/m2K
  • Windows (uninstalled) should have a U value of <= 0.8 W/m2K, with a solar energy transmittance (inc frames) of >= 35% and a visible light transmittance (inc frames) >= 50%
  • Rooflights (uninstalled) should have a U value of <= 1.0 W/m2K
  • All habitable areas to have a glazing area (excl frames) >= 14% floor area
  • Typically space is heated with hot water coils within the MVHR ducts
  • MVHR should recover at least 75% of heat, with a fan using <=1.44W per l/s
  • Any non-solar water heating to be Gas Condensing boiler or CHP – wood fired stoves are not permitted (this conflicts with my peak-oil resilience planning)
  • Insulation on water tanks to be at least 100mm PU foam, all pipes and valves to be insulated with at least 40mm mineral fibre, and all cold pipes to have a vapour barrier
  • Lighting to be >= 50lm/W
  • Use the most efficient appliances – A/A+ minimum. TV to be LCD.
  • Use a heavy-duty membrane to air-proof the house.

In conclusion, this is a great list of targets which I may I don’t think I’d go for PassivHaus certification, even though I like the overall aims – my Peak-Oil resilience planning needs things that are proscribed by the standard – like a wood-fired stove!

 PassivHaus Resources

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Get rid of your Tumble Dryer

Rotaire Dryline

Rotaire Dryline

Tumble Driers are a contentious item in the UK green movement – just look at all the debate raging over at Bean Sprouts. And the fact is, that if you don’t have one, but dry inside on radiators, then you’re still going to be using a lot of extra energy to dry your clothes – have a look at the figures here. Now most of the time drying outside in the UK is an impossibility – it’s rainy or even just generally damp. So a bright spark has come up with the wonderful device in the picture – it’s a waterproof cover for a rotary airer. It means that your clothes will dry even on a damp Manchester day – the nets down the side allow the wind through, but prevent the rain being blown onto the clothes.  I’ll certainly try one of these rather than buying a tumble dryer (how the hell would I power a tumble dryer with my Post-Peak-Oil Solar PV 🙂  anyway).

You can get them online from Rotaire from £30.

Underfloor heating or radiators?

UnderFloor Heating- MysonAssuming we’re not going to be at the point of only heating one room anytime soon, how do we heat the whole house? Traditionally I’d have said easy – just radiators. The hot water can come from our wood-fired range, topped up with Solar hot water  and our emergency Gas boiler. But I’ve always had a hankering for underfloor heating, so I thought I’d have a look and see whether it was possible , and economically sensible.

The efficiency figures are impressive – “wet” underfloor heating is 30% more efficient than radiators (you can also get electric underfloor heating but it is 30-40% more expensive to run than the hot water – “wet” – systems, so we won’t be considering those).

Wet systems work by running warm water through a network of pipes either under the floor or under the floor covering. The water only has to be about 50C, so it’s much easier to run with renewable sources than radiators are. You’ll also get back all the wall space usually dedicated to radiators, and benefit from not having your heating source trapped behind a sofa or right underneath a window.

I’ve always thought it’d be something you’d only fit if you were building new or replacing all the floors, but there are now systems that will fit on top of your existing floor, under your floor covering. This makes fitting them to an existing house a much more manageable proposition. You just need to ensure that suspended ground floors are insulated and that you don’t have too insulating a floor covering – make sure it is less than 1.5 tog.

How much will it cost? If you’re doing a whole house it’ll probably come in at between £12-16/sqm – about the price of a decent carpet, ro about the same price as a radiator system. So you probably wouldn’t do it to replace a perfectly good central heating system, but if you need all-new heating it should definitely be considered. They should last 25-50 years so it’ll be a good investment!

Other resources

  • Channel4 – a great discussion of all the options and issues. 
  • Myson – Manufacturer, will lots of great technical information on what’s possible, prices etc. Check out their great Technical Guide.
  • Polypipe – Manufacturer, includes details of their Overlay low-profile over-floor system.
  • SelfBuildABC.co.uk – great article on all the issues.
  • Borders Underfloor Heating – a supplier with diagrams of all the fitting methods for each floor type.

Resilience: Woodburning Stoves for Heating & Hot Water

Thermal Store from BoilerStoves

Thermal Store from BoilerStoves

A lot of time is spent discussing how we’re going to stay warm after the peak, and increasingly people are installing woodburning stoves and / or solar hot water systems  as a part of their solution for heating and hot water. There is a great discussion on this over at Powerswitch and a whole heap of useful links:

Multi-Fuel Stoves with Backboilers

These can burn wood, coal, and a whole range of other combustibles. They have BackBoilers – literally a boiler attached to the back of the stove – to heat water for radiators / hot water.

Gravity-fed Boiler Systems

You can use a pump to get the hot water from your stove-back boiler to the hot water tank, but if the pump fails then you are at rick of damaging the boiler. A simpler way is to use a gravity fed layout, which work on the basis that hot water rises:

 Solar Systems

For even greater resilience we’d have multiple options for hot water and heating. Pairing a Sola Hot Water system with a woodburning stove makes a lot of sense – Solar works best in the summer when you don’t want the stove heating up the house, and in Winter the heat of the stove is a welcome side-effect.

Hot-Water Cylinders and Thermal Stores

These have changed a lot since I was a kid, when we had a big coppery tank in the Airing Cupboard with a thin, patchy red jacket strapped onto it for insulation! Now there’s a whole range available with cast-over insulation, and – essential for our resilient system – multiple inputs. So you can plumb several heat sources into the one tank: Solar, Gas, Electric, or Solid Fuel. A Thermal Store (or Heat Accumulator) is a good way of making the most of your solar and wood-fired hot water. Think of it as a huge hot water tank that can take all the heat your stove can throw at it while going at its most efficient, fast, burn.

Online Tools and Calculators

There are some great calculators available online to help you work out the heating requirements of your house, and to help you design and layout your system: 

  • Tuscan Foundry Calculator – great for calculating the heating required per room
  • idhee – Calculator for ensuring that you get the correct size boiler
  • Heatweb – great schematic designer and calculator for specifying system components

Flues

Short, or poorly-insulated flues seem to cause many problems for woodfired stoves – causing them to let smoke into the room among others.

  • Flue Systems – supply everything your flue may need, including insulated twin-wall flues, chimney fans and cowls.

Well that’s enough background to get started – I’ll add more when I’ve worked out what we’re going to do!

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